1. Field of the Present Invention
The present invention relates to a flexible flat cable (FFC) applicable to low voltage differential signaling interfaces, more particularly a flat flexible cable (FFC) having a characteristic impedance (Z0) of 100Ω±5% to be used in a low voltage differential signaling (LVDS) signal transmission system.
2. Description of Prior Act
Referring to FIGS. 1 and 2, since a large volume and a high frequency of signal transmissions occur between the liquid crystal display (LCD) and the main system, therefore the present high-frequency signal transmission system constructed between a liquid crystal display interface 10 and a system board interface 20 adopts the low voltage differential signaling (LVDS) receiver featuring a high speed at 1.4 Gb/s, a low power consumption and a low electromagnetic radiation as the signal transmission interface for the liquid crystal display interface 10. With the connection of a transmission line 15 and the system board interface 20 (that is the socket 22 of the connector on the system board interface 20, signal connection is constituted and a prior LVDS signal transmission system 11 is defined.
However, according to the standard of the LVDS interface defined by the ANSI/TIA/EIA-644-1995, the transmission line 15 used for such LVDS signal transmission system 11 must have a characteristic impedance (Z0) of 100Ω±5% to match up with the impedance (Z) of the circuits of liquid crystal display interface 10 and the system board interface 20.
In the meantime, this kind of LVDS signal transmission system 11 must meet this requirement to lower the electromagnetic interference and eliminate noise interference in order to correctly carry out the signal transmission between the liquid crystal display interface (hereinafter referred as LCD interface) 10 and the system board interface 20 or avoid producing errors, otherwise a signal reflection and a noise interference will be produced in the signal transmission between the LCD interface 10 and the system board interface 20 and cause loss, deformation or distortion of signals.
The transmission line 15 suitable for being used in the prior LVDS signal transmission system 11 includes the traditional wire cable having a characteristic impedance (Z0) of 100Ω±5%, a flexible printed circuit, or a mini coaxial cable, etc.
However, the prior flexible flat cable has a simple structure and a lower cost, but its characteristic impedance is approximately 130 Ω which is not in compliance with the standard and specification of the LVDS signal transmission system 11. Therefore, this kind of flexible flat cable is not applicable for the prior LVDS signal transmission system 11.
Further, the transmission line 15 used for the prior signal transmission system 11 as shown in FIGS. 1 and 2 must have a LVDS connector 14 at one end of the transmission line 15 for connecting the LVDS receiver 12 of the LCD interface 10, and the other end of the same transmission line 15 must have a plug (or a socket) 24 for connecting a socket (or a plug) of the system board interface. After the LVDS connector 14 at one end of the transmission line 15 and the LVDS receiver 12 of the LCD interface 10 are connected, the connector 24 at the other end is electrically connected with the connector 22 of the system board interface 20 to define a prior LVDS signal transmission system 11 between the LCD interface 10 and the system board interface 20.
In other words, the prior LVDS signal transmission system 11 currently used for transmitting signals between the LCD interface 10 and the system board interface 20 is a LVDS signal transmission system comprising five components including a LVDS receiver 12, a LVDS connector 14, a transmission line 15 having a characteristic impedance of 100Ω, a plug of the connector 24 and a socket 22 of the connector. As to the cost, the inventor of the present invention believes that such prior LVDS signal transmission system 11 has more components and requires a more expensive transmission line 15, and thus the prior needs further improvements.
In the solutions for reducing the quantity of components and lowering the cost, some manufacturers improve the aforementioned transmission line by improving the flexible printed circuit (FPC) by means of building the plug or socket directly on both ends of the flexible printed circuit, and thus it no longer needs to build additional plugs or sockets for the connector of the flexible printed circuit (FPC), but electrically connect the connector. Such arrangement can achieve the objectives of reducing the quantity of components and lowering the cost.
A prior flexible connector 33 disclosed in U.S. Pat. No. 6,743,045 is as shown in FIG. 3. The flexible connector 33 has an insulator 35 which is coupled individually on a position proximate to both ends, both ends of the flexible connector 33 constitute a structure similar to the plug of a connector, and thus it is not necessary to build additional plugs or sockets for connecting the flexible connector 33 to be used together with a socket 36 of the connector of a first printed circuit board 31 and a socket 37 of the connector of a second printed circuit board 31 and define a signal transmission system.
Although such signal transmission system can achieve the objective of lowering costs, it is still a signal transmission system that requires five components comprising a flexible connector 33, a socket 36 for the connector of a first printed circuit board 31, a socket 37 for the connector of a second printed circuit board 31, and two couplers for coupling an insulator 35 disposed on both sides of the flexible connector 33. Therefore, such signal transmission system still needs further improvements for reducing the quantity of components.
Particularly in the area of the prior flexible connector, a prior flexible flat cable has not been taught explicitly or implicitly to be used in the prior LVDS signal transmission system 11.
Thus, if the characteristic impedance (Z0) of a prior flexible flat cable having a simple structure and a low cost can be adjusted and accurately limited to about 100Ω, then such flexible flat cable mot only can satisfy the requirements of the standard and specifications of the LVDS signal transmission system 11 and greatly save the manufacturing cost of the LVDS transmission line, but also can offer a new application to the prior flexible flat cable by using the prior flexible as the LVDS transmission wire which breaks through the biased view of the flexible flat cable not applicable to be used as the LVDS transmission line. In the meantime, the LVDS signal transmission system adopting this kind of flexible flat cable can be developed, so that the objectives can be achieved for reducing the quantity of components and lowering the cost of the LVDS signal transmission system.